92 tbi 350 rebuild or repower ?

[rickpilgrim]

The 92 truck has low oil psi when at operating temp. Even with the new sealed power oil pump and 10w-30 the highest is 28-30 psi and 10psi at idle. Under full throttle when you get past 3500rpm you can hear a faint rattle. That and a quart of oil every 250-300 mi. It starts and runs awesome and has decent power with no check engine light though.
Now I have an unknown 95 K2500 350 that was supposed to run good 2 owners ago, could rebuild that long block, but can I cam it without tbi/ ign mods?
I also have a good 98 5.7 4 bolt main vortec that runs nice and has awesome oil
Pressure on 5w-30, can I make a tbi vortec engine?
Thoughts anyone?

[Marv D]

Rick have you checked the gauge and verified it really IS low oil pressure. My 94 dash gauges are 'old and tired' (like me) but are CRAZY inaccurate. Temp shows ~150 at 180, Oil PSI shows 75 when at 55psi, and volts,, ... well ya just never know, anywhere in the sweep from 8-15 is ' normal'. I added a set of pillar gauges with a trio of Autometer gauges and they are not 'perfect' but at least consistant. The stepper motors in the stock dash get horribly 'crazy' when they are old and tired. (again probably more like me than I care to admit)

ONE thing to keep in mind here,,, 5-30 oil is a 5wt oil, with polimers that tend to 'string together' and make the oil act like a 30wt oil at 'normal' engine temps (200-240°) The idea is to have the grat flow capabilities of a 5wt oil when cold,, and 30wt when hot. That said,, the additive package that is supposed to make that happen is SUPER high-tech stuff added to a 5wt oil. The better the quality of the aditive package the better this 'morph to 30wt happens. I'm still not convinced it really does 'change' to 30W I mean I look at it this way. IF it did exactly what the 'theory' says it is supposed to do, it would have the same oil PSI cold as it does HOT.
When internal components overheat due to lack of lubrication, the expand, you get metal transfer and cold welding till things simply seize. My thought is components are all expanding and oil clearances do grow, without a doubt bu tthe oil PSI drop (cold to hot) is JUST AS MUCH the oil's fault as it is loose components. Loose oil clearances allow the THIN oil to escape more easily.

That said,, IF your gauge is verified and right.... try a 40wt diesel oil and see what happens. All of the discount houses have a 'house' brand, as does Dello and Rotella are offered in straight 40wt

As far as changes to the motor,, If you keep the TBI your going to have a PIG unless you have a new prom burned for the OBDI ECM And TRUST ME on this,, finding someone that knows what the heck they are doing and can get you a GOOD tune is hard (if not IMPOSSIBLE) to find these days. Even the chips to burn are getting difficult to find a source from what I hear. I did to my 94 4x4 what your considering and believe me,, if I had it to do again,, NO WAY, I'd toss the TBI and ECM driven distributor and put a stinking CARB on it. WAY cheaper and WAY easier to change the tune.

For my 94 I used a later 1piece rear seal block so I could move to a hudraulic ROLLER (I refuse to build a flat tappet ANYTHING any more) , did a 3.75" stroke (383), Coated Mahle forged pistons, Scatt I-beam rods ,bought a set of RHS Iron vortec heads, Had a GMPP Vortec / TBI intake bored to accept a 670CFM Holley throttle body, (at the time that was the ONLY Vortec TBI intake available, but now I believe there is a knock-off available for WAY less than the $400 the GMPP were then)
All in all I think I spent right at $5500 building a BAD Dawg 4x4 Vortec stroker TOWING motor. THEN came 4 different chips trying to get the stupid thing to run right.

ALL that considered,,, Throw a long block at it with a fresh TBI and enjoy the simplicity of what you have. OR if your exempt from emmissions and inspections, throw a carburated 383 at it with a MILD cam if you really want to make enough torque to shred the 25year old trans and differential.

[kennyhammond]

I am not wanting to steal the thread but I am also curious on a good build or replacement around this year model Far as tbi I was thinking of dropping it and maybe going with something else ...for ,e I am using it as a work truck but want the dependable side to start every time I rember as a kid having to pump the peddle for the carb to start ....

[Kudzupatch]

I have been digging into this as I am going to be replacing mine in the near future. My conclusion is, it is cheaper in the long run to buy a GM crate motor with a warranty then build one yourself. A quick run of the numbers in my area, with the machine work the cost is about even. And there is no warranty on my work.

If you are going to change anything in the engine, you need to change the 'tune'. I am going to put in the latter model Vortec and that by all means requires a tune to match the engine. Lots of horror stories of people builind engines with Vortec heads, cams, etc and they run worse than before but they are trying to run the stock tune on a modified engine. Typically they are trying to tune an engine by mail order because no one here is working with the OBD1 anymore. I had about decided to just buy a stock replacement engine.

Then I discovered Moates Ostrich, it replaces the chip in the computer and can be connected to most software and tuned like the new computers. Any tuner, if they are willing, could tune it for you. The idea is once it is right, you get someone to burn you a chip and replace the Ostrich, but many just keep in place.

This is the way I am going go. I will buying an Ostrich and a crate Vortec and use my TBI. If I have too, I will tune it myself but hoping to get one of the local guys to do it for me.

[rickpilgrim]

Ok, straight wt 40 oil improved it to 35-38 psi warm hwy and 12-15 at idle so I know the tbi 350 is warn out. No surprise to me, it came without an air cleaner and very filthy oil but again, $500 1992-K2500 truck with an 10 month old/367x. mi goodwrench trans work order that started and ran out strong that was ok.
When I was talking about rebuilding the 95 parts truck 350 and putting in a cam I was thing mild RV type cam to help bottom end power a bit. No stroker, aftermarket heads or street/strip cam.
I have a good 98 vortec 5.7 4 bolt main in a bad frame/trans plow truck. Ideal would be to take that engine and the gmpp intake/egr valve and piping and exhaust to muffler and put it in the 92. I can see more fuel pressure but do I really need a re flashed ecm and everything else for a box stock vortec 350 to run with tbi?

[Kudzupatch]

Originally Posted by rickpilgrim

I have a good 98 vortec 5.7......but do I really need a re flashed ecm and everything else for a box stock vortec 350 to run with tbi?

Yes. Vortec will has much better flowing heads, some of the best stock Chevy heads and a different cam. Your existing TBI is tuned to match a very different engine.

You have to remember that the computers are tuned very specifically to the needs of the motor that is in the car. Change anything that changes air flow or fuel flow and it changes the requirements of timing and fuel. Going to Vortec heads is not a small adjustment, it is major improvement.

[Marv D]

Ditto:

The Swirl port heads of the late 80's to mid 90's were great at making torque from idle to about 3500rpm, then they were all done. And lets be honest,,, how often are you really above 3500RPM??? GM decided a work truck didn't need HP (= RPM capabilities) it needed TORQUE from idle to 3000RPM and the 'LO' motors at 190-210 HP (but 350+ # of torque in a low RPM range) did that well. It didn't need a very smart ECM to manage the TBI with just 2 injectors in a throttle body and the prom was flashed specifically for the motor / chassis / tune.

The batchfire 8 injectors of the 96-2000 Vortec motor and OBD II TOTALLY re-vamped engine management, heads and compression, cam and needed a much smarter brain.

Then came the LS with cam sync / sequential port injection and the ECM continues to get smarter and smarter.....


What I'm getting at is the OBD I computer of the 80's to 95 was BARELY one step above a carburetor,, and then ONLY in attempting to reduce emmissions and cut power output so efficiency was 'controlled' . When they put a rev limit in the ECM GM saw $ signs because it simply wouldn't rev high enough to blow up. So think of the engine management system for the TBI as a FIXED, un-tunable carb with a FIXED timing curve. You can't make significant changes in the way the engine responds to throttle (cam and compression) because the dumb box controlling things just does't understand what's happening when feedback gets out of range of it's 'expected' feedback.

[rickpilgrim]

Seeing we can't keep the stock tbi with a vortec 5.7 and I really don't want to try to transplant the 98 ecm for the 5.7/4L80E and wiring to the 92 will the 95 tbi 350 bored .040 and the stock replacement "929" cam work with the 92 tbi system?

[Kudzupatch]

If it has the newer 'vortec' heads, again, it will work but you are really going to need to adjust the tuning and have a new chip burned. I am no expert but as i said I have been researching the options for months now, reading everything I can find.

From what I am reading the new heads need a very different timing curve and since they have a better flow, you need to adjust the fuel curve too. Cam is important but there is more involved than just the cam.

All my reading has lead me to the conclusion that the best way is buying the Ostrich Emulator and then it can be tuned on the computer while running, much like the new ECMs. So anyone that tunes engines can do it without having to burn chips for you. Once you get it right, you can send that computer file by email to somone and have a chip made and sell the Ostrich if you wanted.

[rickpilgrim]

Adding up the cost involved for swapping a good vortec 5.7 vs rebuilding the 95 tbi is looking more and more like the 95 wins in a cost and no tuning needed vs trying to find time around here for tuning.
I got a good lesson in that last week when the Dually's Optishift trans controller failed. It took 4 days to get a replacement Optishift, 5 min to install and 3- 1 hr sessions to tune it.
Thank You to all for the good advise!

[Kudzupatch]

Totally get it! I have been back and forth and since I am looking at a Suburban I still keep thinking going replacement crate motor. But it is just so underpowered... at least for my tastes.

Then I tell myself I drive slow 99% of the time and rarely tow anything heavy. But I like to tinker and want to know more about turning. I am going to keep this one so I am going Vortec. That is about 40 plus HP over the original. I would just like to see it be able spin the tires. :-)